1. Field of the Invention
The present invention relates to an optical receiver, in particular, the invention relates to an optical receiver that receives optical signals with a multiple transmission speed.
2. Related Prior Art
Recently, various transmission speeds are applied in the optical communication, accordingly, it becomes difficult to attain an acceptable error rate for the transmission without matching the performance of the optical receiver, especially, the sensitivity and the frequency bandwidth of the pre-amplifier with the transmission speed. The Japanese patent published as H11-340745A has disclosed an optical receiver that escapes from the saturation of the output thereof by varying the feedback resistance of the pre-amplifier, which is connected in parallel to the inverting amplifier to amplify a faint signal output from the light-receiving device, depending on the output level of this inverting amplifier.
However, the optical receiver disclosed in the patent, because the gain of the inverting amplifier depends on the output level thereof, the performance of the amplifier is not always fit to the transmission speed. That is, even if the saturation of the output level may be prevented, the gain and the frequency bandwidth thereof are not always set to values adequate to the transmission speed of the communication.
A control signal may be externally provided to control the sensitivity, the gain and the frequency bandwidth, of the optical receiver. However, such configuration requires an additional lead pin to transmit the control signal in the package of the optical receiver, which brings the up-scaled package. Without making the electronic circuits installed within the package small, the optical receiver is hard to be shrunk.
The present invention is to provide an optical receiver that enables to vary its performance, especially, the gain and the frequency bandwidth, depending on the transmission speed of the communication with a simple arrangement.